▎ 摘　　要

We report the electrical transport properties of a dual-gate graphene device placed on a CaF2 substrate. A hexagonal boron nitride top-gate dielectric was introduced to confirm the electrical characteristics of the CaF2/graphene transistor because it is difficult to inject sufficient carriers through the CaF2 substrate owing to its thickness of 500 mu m, and the typical ambipolar behavior of graphene with a slight n-doping effect was clearly observed. In addition, we used a polymethyl methacrylate (PMMA) film as a top-gate dielectric for large-scale graphene devices grown via chemical vapor deposition, which was transferred onto a CaF2 substrate. We controlled the high gate leakage current caused by the breakdown of the polymer due to non-uniformity by applying the film-transfer process rather than the direct coating method on the graphene device. Furthermore, the transport properties of large-area graphene in contact with CaF2 are discussed with respect to the effect of top-contacted PMMA.